1. Field of the Invention
This invention relates to modified polyester compounds and is more particularly concerned with blends of polyalkylene terephthalates with segmented polyester amides.
2. Description of the Prior Art
Polyalkylene terephthalates are well-known in the art and are described, for example, in U.S. Pat. Nos. 2,465,319 and 3,047,539. The polyalkylene terephthalates are particularly advantageous as film and fiber forming materials and more recently have become important as resins for use in the preparation of finished products by injection molding. Of these various polyesters polyethylene terephthalate, polybutylene terephthalate, and blends of the two are the most frequently employed materials. However, the crystallization rates of these polyesters, especially those of polyethylene terephthalate, are undesirably low. In order to achieve maximum properties in molded parts it is necessary to maintain the part in the mold until crystallization has taken place fully. Because the crystallization rates are relatively slow, this means that the time required for a complete mold cycle is also correspondingly high compared with other plastics.
A wide variety of methods of improving the rate of crystallization has been described in the art. Such methods include incorporation of nucleating agents, such as finely divided solid inorganic materials, and blending with other polymers such as polyacrylates. Illustrative of these methods are those described in U.S. Pat. Nos. 4,401,792 and 4,404,161.
We have now found that, by incorporating into the polyalkylene terephthalate minor amounts of certain segmented polyester amides, it is possible not only to increase significantly the rate of crystallization of polyesters but also in many cases to improve markedly the impact resistance of the polyesters and thereby render them useful as suitable materials for the preparation of a wide variety of structural components.